PROJECT SUMMARY ABSTRACT Although interactions between the senses of smell and taste are a key factor for guiding food choices, the neural mechanisms underlying the multisensory integration of odors and tastes remain largely unknown. A more thorough understanding of these neurobiological processes will provide better insight into diseases characterized by unhealthy food choices, such as obesity or diabetes. Eating food simultaneously activates the olfactory and gustatory systems to generate enduring odor-taste associations. The primary cortical area for taste, gustatory cortex (GC), is a principal site of convergent gustatory and olfactory information. Recent work from our lab determined that functionally distinct populations of neurons in GC represent different properties of individual unpaired odors or tastes. However, how neurons in GC represent odor-taste mixtures, as well as the neural mechanisms that underlie integration and processing of smell and taste remain unclear. Recent behavioral and physiological studies show that cortico-cortical interactions between sensory cortices are fundamental to multisensory integration, suggesting that projections from the functionally distinct anterior (aPC) and posterior (pPC) regions of piriform cortex (i.e., olfactory cortex) modulate multimodal chemosensory processing in GC. Using rats as a model system, this proposal will combine behaving electrophysiology and optogenetic techniques to investigate how the circuit between neurons in GC and the functionally distinct regions of piriform cortex mediates multisensory integration of odors and tastes. The Specific Aims will test the following hypotheses: Aim 1: Different populations of neurons in GC encode the chemical identity and hedonic value of odor-taste mixtures. Aim 2: Neurons in GC that respond to both odors and tastes receive aPC input representing the chemical identity of odor-taste mixtures. Aim 3: Neurons in GC that respond to both odors and tastes receive pPC input representing the hedonic value of odors and odor-taste mixtures. The results of each Specific Aim will contribute fundamental knowledge about the cortico-cortical circuitry underlying the integration of smell and taste and provide a necessary prelude for investigating the role that these cortico-cortical circuits play in guiding food choices.